1. Field of the Invention
The present invention relates to an accumulator fuel injection system, and more particularly to an accumulator fuel injection system which enables the accumulation and injection of high pressure fuel.
2. Description of the Related Art
A conventional accumulator fuel injection system is typically provided with, for example, a low pressure pump (low pressure fuel supply pump) which delivers fuel under pressure from a fuel tank, a high pressure pump (fuel injection device) which changes the fuel from the low pressure pump into high pressure fuel, an accumulator (common rail) which accumulates the high pressure fuel from the high pressure pump at a predetermined pressure, an injector which is connected to the accumulator and which injects the high pressure fuel, and a pressure increasing unit which is provided between the injector and the accumulator and which further increases the pressure of the high pressure fuel. A common rail comprising a pressure increasing unit is known as a pressure increasing common rail.
This pressure increasing unit and pressure increasing common rail employ a piston system, for example, in which the pressure of the fuel from the high pressure pump is increased in accordance with the area ratio between the pressure increasing side at which the piston has a large diameter and the pressure increase receiving side at which the piston has a small diameter, whereupon the fuel is supplied to an accumulator for high pressure fuel injection.
When this pressure increasing operation is performed using fuel from the high pressure pump, leaked fuel is returned from the fuel increasing unit and the injector to the low pressure side (a fuel tank at atmospheric pressure), and the amount of fuel recirculation that must be performed is large, for example a recirculation amount of up to three times the amount of injected fuel.
Hence in an accumulator fuel injection system comprising this type of fuel increasing unit, a problem arises regarding leaked fuel from the pressure increasing unit in that a large capacity high pressure pump and low pressure pump must be provided in order to recirculate a large amount of fuel from the low pressure side to the high pressure side.
Furthermore, leaked fuel from the pressure increasing unit and the injector reaches extremely high temperatures and if left as is, may damage the high pressure pump and so on. Further problems include the fact that changes in the kinematic viscosity of the fuel caused by temperature change may contribute to changes in the injection amount.
The present invention has been designed in consideration of such problems, and it is an object thereof to provide an accumulator fuel injection system which is capable of recirculating leaked fuel from a high pressure side to a low pressure side.
Another object of the present invention is to provide an accumulator fuel injection system which comprises a fuel increasing unit and a fuel increasing common rail and which is capable of reducing the amount of fuel that must be delivered under pressure by a low pressure pump.
A further object of the present invention is to provide an accumulator fuel injection system in which a low pressure fuel supplying pump does not have to be increased in size in order to recirculate large amounts of leaked fuel from the fuel increasing unit.
A further object of the present invention is to provide an accumulator fuel injection system which is capable of cooling the temperature of leaked fuel from the fuel increasing unit, injector, and so on.
More specifically, the object of the present invention is to return high pressure leaked fuel between a low pressure pump and a high pressure pump, and also to cause a filter for leaked fuel to function doubly as a cooling device. The present invention is an accumulator fuel injection system comprising a low pressure pump for delivering fuel under pressure from a fuel tank, a high pressure pump for changing the fuel from the low pressure pump into high pressure fuel, an accumulator for accumulating the high pressure fuel from the high pressure pump at a predetermined pressure, an injector which is connected to the accumulator for injecting the high pressure fuel, and a pressure increasing unit which is provided between the injector and the accumulator for further increasing the pressure of the high pressure fuel. This accumulator fuel injection system enables leaked fuel from the pressure increasing unit to be recirculated to the downstream side of the low pressure pump through a unit leakage passage.
A main filter is provided on a low pressure fuel passage between the low pressure pump and the high pressure pump, and the unit leakage passage may be connected to the low pressure fuel passage between the low pressure pump and the main filter.
The main filter is provided on the low pressure fuel passage between the low pressure pump and the high pressure pump, the unit leakage passage is connected between the main filter and the high pressure pump, and a cooling filter unit may be provided on the unit leakage passage.
A mechanism, such as an air cooling system or a water cooling system, may be employed at will as the leaked fuel cooling system used in the cooling filter unit.
In the accumulator fuel injection system according to the present invention, high pressure leaked fuel is returned between the low pressure pump and high pressure pump, or in other words leaked fuel is refluxed to the downstream side of the low pressure pump, and as a result the amount of fuel that must be delivered from the low pressure pump toward the high pressure pump can be reduced. Thus, even with a pressure increasing common rail, the capacity of the low pressure pump does not have to be increased.
Further, by causing the leaked fuel filter provided on the unit leakage passage to function doubly as a cooling device, leaked fuel can be cooled to reduce the temperature thereof and thereby avoid adverse effects on the system as a whole.